Many processes for shaping metal, wood or other materials involve the removal of material by cutting or similar operations. The tools used to perform the cutting operations are made of special steels (tool steels), hard metals (cemented carbide alloys), oxide ceramic materials and diamonds.
Two of the most important machining processes are turning and boring. Turning is the process of reducing the diameter of material held in a lathe. The piece of material as a workpiece is attached to a driven spindle and, while rotating, is brought into contact with a cutting or turning tool. The position of the tool in relation to the axis of rotation is varied to cut the workpiece to the desired shape. The cutting may be on an external or internal surface of the workpiece.
Boring, or more generally drilling, is a rotary cutting operation for producing holes in the desired material. The boring tool provides a cutting edge which while rotating is fed forward under pressure into the subject material. Alternatively, a bar feed machine is used which holds the boring tool stationary and enables the material to be applied to the tool while the material is rotated. Different boring tools (i.e. cutting edges of a boring tool) produce holes of different diameters and lengths. Holes in the range of about 0.02 inch to about 1 inch diameter and 0.1 inch to about 11/4 inches in length are typically produced.
Turning and boring tools are available in a wide range of shapes and types. Generally, the tool has a handle or shaft serially connected to a shank to form what is commonly referred to as a boring bar or turning holder. The distal or head end of the shank provides the cutting edge or an attached cutting tip. Typically the handle and shank are formed of high carbon steel, hardened and tempered. Alloys known as high-speed steels are used for tools that are operated at relatively high cutting speeds. The cutting tip is made of a cemented carbide, for example, or particularly tungsten carbide.
In recent years, small carbide inserts have been employed on boring bars or turning holders for metal removal. The carbide insert is generally triangular or square in shape with a hole through the center. A screw passes through the hole into the distal end of the bar/holder to fasten the carbide insert thereto. The insert is positioned such that one corner of the insert is "exposed" and used as a cutting edge. As the corner is worn to the point of no longer being effective, the screw is loosened and the insert is rotated to position and expose an unused corner for cutting. The screw is retightened and the tool is ready to use. This process is repeated until all the corners are dull. The insert is then replaced.
One disadvantage of these insert cutting tools is that the screw may become loose during operation of the tool, resulting in slippage of the insert and ineffective machining. Many tool manufacturers have added a small clamp in addition to the screw to assist in securing the insert on a turning holder. However, such a clamp in boring tools is impractical since there is a lack of space for the clamp. That is, a boring bar usually functions within the confines of a hole not much larger in diameter than the diameter of the boring bar itself. Hence, the added bulk of a clamp is inconsistent with the minimization of boring bar dimensions to enable use in constricted areas.